Stabilizers are used in a drill string to provide a predetermined radial spacing of the longitudinal axis of a component of the drill string with respect to the wall of the wellbore in which the drill string is disposed. A stabilizer may be either full-gauge, so that the outer diameter of its blades is substantially the same as the gauge diameter of the drill bit, or under-gauge, so that the outer diameter of its blades is less than the gauge diameter of the drill bit. The use of various combinations of full and/or under-gauge stabilizers, and the longitudinal spacing thereof along the drill string above the drill bit, is one of various methods which may be used to control the direction the wellbore takes during drilling.
One or more components of the drill string may include sensors and/or other measuring tools operable to measure a characteristic property of the formation penetrated by the wellbore. If a stabilizer is used, one or more of such sensors may be positioned underneath the blades of the stabilizer in a manner permitting a clear path for the sensor signal to reach the formation. The blades permit wellbore fluids and/or drilling debris to travel past the stabilizer while providing a measurement space or standoff that is substantially free of these and other obstructions, which otherwise may have an adverse impact on the quality of the measurement. The stabilizer may also include a window or other area transparent to sensor measurement signals emitted by the sensors located within the drill collar, thus providing a clear path for the sensor signal to reach and/or return from the formation. In such implementations, the stabilizer sleeve is axially and rotationally positioned such that the window is in front of or otherwise aligned with the sensor contained within the collar. The stabilizer sleeve is maintained in such position during drilling.
Certain slide-on stabilizers and corresponding drill collars may be mechanically compromised by fatigue and other reliability issues, and can be difficult to manufacture. For example, the slide-on stabilizers, such as keyed and spline type stabilizers, may experience high cyclic loading caused by rotation and bending while drilling, resulting in adverse wear and deformation, which may induce early catastrophic failures.